High frequency vacuum tube energy coupler

ABSTRACT

A high frequency transmission line coupler for transfer of propagating high frequency energy with respect to the interior of a high frequency vacuum tube is characterized by a rugged vacuum envelope system permitting transfer of high power with freedom from the development of electrical arcs and cracking and leaking of vacuum seals. The structure eliminates the need for making a vacuum seal at the inner conductor of the coupling transmission line element and provides greatly increased tolerance to thermal and other shock mechanisms.

United States Patent Rawls, Jr.

1 1 Dec. 26, 1972 men FREQUENCY VACUUM TUBE ENERGY COUPLER John L. Rnwls, Jr., Archer, Fla.

Assignee: Sperry Rand Corporation Filed: March 10, 1971 Appl. No.: 122,877

Inventor:

US. Cl. ..315/3.5, 315/3953, 333/25, 333/34 Int. Cl.....- .1101] 25/34 Field of Search ..315/39.53, 3.5; 333/25, 26, 333/34 References Cited UNITED STATES PATENTS 6/1959 Cohn ..333/34 X 1/1960 Dench ..333/34 12/1957 Pease ..3l5/39.53 X

2/1965 Eason ..333/26 3,448,331 6/1969 C0ok.... ..3l5/39.53 2,429,291 10/1947 Okress ..315/39.53

Primary Examiner-Herman Karl Saalba'ch Assistant Examiner-Saxfield Chatmon, Jr. Attorney-S. C. Yeaton [5 7 ABSTRACT A high frequency transmission line coupler for transfer of propagating high frequency energy with respect to the interior ,of a high frequency vacuum tube is characterized by a rugged vacuum envelope system permitting transfer of high power with freedom from the development of electrical arcs and cracking and leaking of vacuum seals. The structure eliminates the need for making a vacuum seal at the inner conductor of the coupling transmission line element and provides greatly increased tolerance to thermal and other shock mechanisms.

7 Claims, 2 Drawing Figures PATENTEDums 1912 RS 0L rw MA n mi M r B ATTORNEY HIGH FREQUENCY VACUUM TUBE ENERGY COUPLER BACKGROUND OF THE INVENTION 1 Field of the Invention The invention pertains to means for improving the effectiveness and life-time of operation of power electron tubes and more particularly concerns a rugged, shock-proof transmission line energy coupler means for application in high power, high frequency vacuum tubes.

2. Description of the Prior Art Generally, prior art transmission line input and output couplers for high frequency amplifier, oscillator, and other vacuum tubes are of the hollow wave guide or of the coaxial transmission line types. Both types require the use of glass or ceramic seals so as to complete the vacuum envelope of the tube. Coaxial line systems are often chosen because of their relatively wide band characteristics for use in broad band, high frequency tubes, such as traveling wave tubes, or in high frequency vacuum tubes having wide tuning ranges.

Prior art coaxial line energy couplers for vacuum tubes generally are constructed with two glass-to-metal seals; one seal is made between a glass vacuum barrier and the inner wall of the outer conductor of the coaxial line and a second seal is made between the glass barrier and the outer wall of the inner conductor of the coaxial line. In addition to requiring the steps involved in making two seals, such designs are fragile and susceptible to damage in handling. Also, at high altitudes or in other adverse atmospheric conditions, such designs exhibit arcing between inner and outer conductors, especially at the exterior surface of the glass or ceramic barrier of which the seals are formed. Mechanical or thermal shock, such as produced when arcing occurs, often leads to damage of the seal, cracking the barrier material and causing leakage and consequent destruction of the tube.

SUMMARY OF THE INVENTION The present invention relates to rugged high frequency transmission line structures for transferring high frequency energy with respect to the active circuits contained within the vacuum envelopes of high frequency vacuum tubes, such as traveling wave, klystron, magnetron, and other such vacuum tubes. The energy coupling transmission line is provided with a rugged vacuum envelope element permitting transfer of power at relatively high levels with freedom from the development of high frequency arcs adjacent the vacuum envelope element and its associated seals to metal parts of the tube, thus eliminating consequent cracking of the seal material. Further, the structure is simpler than prior art configurations, eliminating the need for making a vacuum seal at the inner conductor of the coaxial transmission line coupler.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, partly in cross section, of one embodiment of the invention.

FIG. 2 is a view similar to that of FIG. 1, showing an alternative construction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, the novel vacuum tube'high frequency transmission line coupling is illustrated as connected to a section of a conventional electron beam helix traveling waveamplifier or oscillator tube, which tube may be of the general type disclosed by Warren D. McBee in the U.S. Pat. No. 2,848,645 for Travelling Wave Tubes, issued Aug. 19, 1958, or in his U.S. Pat. No. 2,887,608 for Travelling Wave Tube, issued May 19, 1959. Both patents are assigned to the Sperry Rand Corporation.

While the novel transmission line coupling is illustrated in FIG. 1 in the location in which it would generally be used for extraction of amplified high frequency energy from the slow wave propagation and amplifying structure of the traveling wave tube, it will be understood by those skilled in the art that the transmission line coupling may also readily be used for inserting energy, for instance, into such a high frequency amplifier, whether of lineal or circular configuration. Likewise, it may readily be adapted for use with other types of high frequency signal generators, including klystrons, lineal and circular magnetrons, high frequency triodes, and other such vacuum tube devices.

It is to be understood that the vacuum tube device shown in FIG. 1 comprises a conventional vacuum tube device with an electron emitting cathode or gun and an apertured anode for accelerating the electron stream formed by the electron gun into the channel formed by the helix slow wave propagation or amplifying structure, which latter may be made of molybdenum. While the electron gun and anode are not shown in the drawings, merely as a matter of convenience, the high power of output section 1 of the helix remote from the cathode-anode structure is shown within the cut away vacuum envelope 2. The helix 1 is shown as a coiled tape, is representative of various slow wave transmission line structures which may be used in traveling wave tubes, and is positioned and held firmly within envelope 2 by conventional dielectric support rods 3, which rods may be made of beryllium oxide and may be equally spaced about the helix and four in number. The character of such helix support systems is well known in the art, having been described, for example, in the aforementioned McBee patents, which also illustrate other representative conventional traveling wave tube elements suitable for use in the present device, including suitable cathode, anode, and signal input structures.

The vacuum envelope 2 surrounding helix 1 is shown supplied with a cold drawn steel flange 4 sealed in vacuum tight relation at interface 5 to a metal support section 6 for support of the novel output transmission line. Support section 6 may be made of oxygen free copper and is supplied with a cylindrical chamber 7 whose axis is aligned with the axis common to helix 1 and helix vacuum envelope 2. Chamber 7 accommodates one set of ends of dielectric rods 3, such as rod end 8. Within chamber 7, rods 3 support the last several turns of helix 1 and also a final distorted helix turn 9 whose purpose is yet to be described.

The wall 10 of support section 6 opposite interface 5 has affixed to it in vacuum tight relation an apertured cold drawn steel circular plate 11, to which is fastened,

also in conventional vacuum tight manner, an. apertured wall 12 forming a spent electron stream entry for the hollow electron-stream collector l3. Electron stream collector 13 may be constructed of a nickelcobalt alloy and may be of the general type discussed in the aforementioned McBee patents or, where high efficiency of operation is desired, may take the form disclosed in the J.L. Rawls US. Pat. application Ser. No. 54,943 for a Depressed Electron Beam Collector, filed July 15, 1970 and assigned to the Sperry Rand Corporation. v r Support section 6 is also an essential part ofthe novel high frequency transmission line coupling, having a circular bore 14 extending radially outward from chamber 7, bore 14 having a slightly enlarged outer section 15. The outer enlarged section '15 accommodates a thin high frequency current conducting tube 16 of a nickelcobalt-iron alloy having a smooth high frequency conducting copper or silver coated interior wall with a diameter substantially the same as that of bore 14. The

bore 14 and wall 17 form a smoothly continuous outer wall portion of a coaxial transmission line. Exterior of support section 6, the outer diameter of tube 16 is increased in steps 18, 19 for purposes yet to be described. The inner conductor of the coaxial line system includ ing bore 14 and wall 17 is formed by the copper or silver coated high frequency current conducting inner conductor 20, which may be made of molybdenum and which lies concentrically within bore 14 and tube 16. At its end adjacent chamber 7, a tapered end of conductor 20 is affixed in high frequency current carrying relation to the unfurled-last turn 9 of helix 1. These latter elements may be permanently joined, for instance, by helium arc welding after placing a 0.002 inch foil of palladium in the joint to act as a filler. A smoothly matched impedance transformation is thus formed between helix 1 and the coaxial line composed of bore 14 and conductor rod 20.

A portion 21 of conductor rod 20 extends into rectangular wave guide transmission line 22 for the purpose of exciting traveling high frequency waves therein. For this purpose, the lower wall 23 of wave guide 22 is supplied with a circular hole, so that the circular stepped portion 19 formed on the end of tube 16 may be accommodated and step portion 19 and guide wall 23 may be fixed together in mechanically rigid relation, as by brazing or by the simple mechanical fastener means to be discussed in connection with FIG. 2, at circular interface 24. Consequently, the portion 21 of inner conductor rod 20, which extends past the end face 25 of step 19, extends into the interior of wave guide 22.

The upper face 25 of step 19 is flush with the inner surface of guide wall 23 and is supplied with a circular depression 26 circularly concentric with rod 20. Sealed in vacuum tight relation within depression 26 is a solid cylinder 27 of low-loss dielectric material. Along the axis of cylinder 27 is provided a bore 28 for accommodating with a loose or sliding fit the end portion 21 of inner conductor 20 which extends into the interior of wave guide 22. The cylinder 27 may be formed of aluminum or beryllium oxide. The upper circular surface 30 of dielectric cylinder 27 is spaced from the interior surface of the upper wall .31 of wave guide 22 and is provided with a circular beveled edge 32. The beveled edge 32 is formed to reduce the'possibility of chipping or cracking due to the sharp edge which would otherwise be present. An end of rectangular wave guide 22 adjacent cylinder 27 is provided with a conventional shorting plate 33 for directing high frequency energy to flow toward utilization apparatus which may be coupled in the conventional manner to wave guide coupling flange 34. The various parts of the wave guide 22 may be constructed, for instance, of copper, brass, aluminum, or steel, with the interior walls of the guide coated with a highfrequency conducting metal after the guide is assembled. A

Whilethe novel high frequency output coupler device may be manufactured in several different ways, the. several bonds may be made as follows. The'permanent joint between bore 15 and thin walled tube 16 may be made in a hydrogen fumace simultaneously with other .similar bonds required in construction of the tube envelope. The bond may bea brazed joint made, for instance, with an alloyof 62.5 percent copper and 37.5 percent gold at a brazing temperature held substantially l0l5 Centigrade for about 10 minutes. Conductor rod 20 is first inserted into outer conductor 16 and the helium arc joint is made between helix turn 9 and inner conductor rod 20.

The beryllium or aluminum oxide cylinder 27 is secured at its base 26 to stepped section 18, 19 by brazing. A convenient method is to heat stepped region 18, 19 using radio frequency induction heating apparatus. The braze material may be an alloy of 28 percent copper and 72 percent gold. The shape of dielectric cylinder 27 is determined by well known design principles generally employed in producing proper impedance matching of a traveling wave tube to its load over a band of possible operating frequencies. The shape of the cylinder 27 is determined by recognizing that both the height and the diameter of cylinder 27 may be selected to effect properimpedance match over various operating frequency bands. 7

It is common practice to supply high frequency energy output devices for use in exciting wave guides which latter are permanent parts of utilization equipment, or for exciting short lengths of guide which are purchased or fabricated separately of the vacuum tube. In lieu of a permanently brazed joint at interface 24 in FIG. 1, the mechanical and separable fastening of FIG. 2 may be employed. In FIG. 2, parts that are the same as those seen in FIG. 1 are supplied with similar reference numerals, including support 6, conducting wall 17, steps 18, 19, inner conductor rod 20 and its end 21, face 25, v

4 depression 26, and dielectric cylinder 27, the bore 28 therewithin, and its upper surface 30. Wave guide 122 is similar to guide 22 of FIG. 1, but is equipped with a clearance hole 143 in its lower wall 123 so that it fits loosely over dielectric cylinder 27.

Wave guide 122 is further provided with a sleeve 141, soldered to wave guide wall 123 concentric with dielectric cylinder 27, and having a threaded outer wall thus firmly affixed to stepped portion 18, 19 when nut 144 is tightened, and therefore is firmly fixed to the vacuum tube both mechanically and in high frequency energy exchanging relationship.

Accordingly, the novel high frequency coupling device represents a versatile design permitting use with permanently attached or detachable configurations and more particularly affording means for the transfer of relatively high power, high frequency energy with respect to high frequency generators and output or input apparatus. The high frequency energy is coupled relative to the vacuum tube and utilization apparatus without the necessity of using a vacuum tight seal around a coaxial line center conductor as is conventionally required. This allows the use of rugged construction, using a scalable cylinder of dielectric material or relatively large size, permitting a single rugged seal over a relatively large metal surface. Simplicity of construction is afforded, along with freedom from the failure modes that damage or destroy vacuum tubes using conventional coaxial line seals. Cracking, leaking, and arcing adjacent a seal to the center conductor rod are eliminated because that seal is eliminated. The novel design particularly overcomes the power handling limitation of prior art coupling systems caused by high electric gradients adjacent the inner conductor that produce arcing across the dielectric surface and cracking of the dielectric material due to excessive thermal stress. The mechanically rugged construction also reduces the risk of damage to the tube during installation or other handling.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the inven- .tion in its broader aspects.

I claim:

1. An electron stream device comprising:

electron stream forming means,

high frequency circuit means in energy exchanging relation with said electron stream, transmission line means in energy exchanging relation with said high frequency circuit means,

vacuum envelope means supporting said electron stream forming means, said high frequency circuit means, and said transmission line means,

said transmission line means comprising first and second concentric high frequency conductor means extending outwardly through said vacuum envelope means,

said first conductor means having an enlarged thick-walled portion remote from said vacuum envelope means and having enlarged planar end surface means substantially perpendicular to said first conductor means,

said second conductor means extending beyond said enlarged planar end surface means, and

solid dielectric means having planar base surface means sealed in vacuum tight relation to said enlarged planar end surface means,

said planar base surface means having an axial bore therein accommodating said second conductor means in sliding fit relation, and said solid dielectric means having a cylindrical diameter substantially greater than said axial bore so as to form a thick dielectric wall directly surrounding said bore.

2. Apparatus as described in claim 1 wherein said solid dielectric means and said second conductor means are adapted to extend within hollow high frequency wave guide means for the purpose of transfer of high frequency energy therewithin.

3. Apparatus as described in claim 2 wherein the height and diameter of said solid dielectric means provide broad band impedance match between said hollow high frequency wave guide means and said concentric transmission line means.

4. Apparatus as described in claim 1 wherein said solid dielectric means comprises beryllium oxide.

5. Apparatus as described in claim 4 wherein:

said first conductor means comprises a ferro-nickel alloy having a high frequency conductive surface coating, and

said second conductor means comprises molybdenum having a high frequency conductive surface coating.

6. Apparatus as described in claim 1 wherein said solid dielectric means has outer surface means opposite said planar base surface means including an annular bevel.

7. Apparatus as described in claim 1 wherein:

said transmission line means comprises helical slow wave propagation means having an end, and

said second conductor is affixed in conductive energy exchanging relation with said ene of said helical wave propagation means.

i i i 

1. An electron stream device comprising: electron stream forming means, high frequency circuit means in energy exchanging relation with said electron stream, transmission line means in energy exchanging relation with said high frequency circuit means, vacuum envelope means supporting said electron stream forming means, said high frequency circuit means, and said transmission line means, said transmission line means comprising first and second concentric high frequency conductor means extending outwardly through said vacuum envelope means, said first conductor means having an enlarged thick-walled portion remote from said vacuum envelope means and having enlarged planar end surface means substantially perpendicular to said first conductor means, said second conductor means extending beyond said enlarged planar end surface means, and solid dielectric means having planar base surface means sealed in vacuum tight relation to said enlarged planar end surface means, said planar base surface means having an axial bore therein accommodating said second conductor means in sliding fit relation, and said solid dielectric means having a cylindrical diameter substantially greater than said axial bore so as to form a thick dielectric wall directly surrounding said bore.
 2. Apparatus as described in claim 1 wherein said solid dielectric means and said second conductor means are adapted to extend within hollow high frequency wave guide means for the purpose of transfer of high frequency energy therewithin.
 3. Apparatus as described in claim 2 wherein the height and diameter of said solid dielectric means provide broad band impedance match between said hollow high frequency wave guide means and said concentric transmission line means.
 4. Apparatus as described in claim 1 wherein said solid dielectric means comprises beryllium oxide.
 5. Apparatus as described in claim 4 wherein: said first conductor means comprises a ferro-nickel alloy having a high frequency conductive surface coating, and said second conductor means comprises molybdenum having a high frequency conductive surface coating.
 6. Apparatus as described in claim 1 wherein said solid dielectric means has outer surface means opposite said planar base surface means including an annular bevel.
 7. Apparatus as described in claim 1 wherein: said transmission line means comprises helical slow wave propagation means having an end, and said second conductor is affixed in conductive energy exchanging relation with said ene of said helical wave propagation means. 